The present invention relates to compositions for optical fiber coatings and fiber optic ribbon matrixes, optical fibers that contain a secondary coating prepared from such compositions, methods of making such optical fibers, and fiber optic ribbons that contain a matrix prepared from such compositions.
Optical fibers have acquired an increasingly important role in field of communications, frequently replacing existing copper wires. This trend has a significant impact in the local area networks (i.e., for fiber-to-home uses), which has seen a vast increase in the usage of optical fibers. Further increases in the use of optical fibers in local loop telephone and cable TV service are expected, as local fiber networks are established to deliver ever greater volumes of information in the form of data, audio, and video signals to residential and commercial users. In addition, use of optical fibers in home and commercial business environments for internal data, voice, and video communications has begun and is expected to increase.
Optical fibers typically contain a glass core and at least two coatings, e.g., a primary (or inner) coating and a secondary (or outer) coating. The primary coating is applied directly to the glass fiber and, when cured, forms a soft, elastic, and compliant material which encapsulates the glass fiber. The primary coating serves as a buffer to cushion and protect the glass fiber core when the fiber is bent, cabled, or spooled The secondary coating is applied over the primary coating and functions as a tough, protective outer layer that prevents damage to the glass fiber during processing and use.
Certain characteristics are desirable for the secondary coating. Before curing, the secondary coating composition should have a suitable viscosity and be capable of curing quickly to enable processing of the optical fiber. After curing, the secondary coating should have the following characteristics: sufficient stiffness to protect the encapsulated, glass fiber yet enough flexibility for handling (i.e., modulus), low water absorption, low tackiness to enable handling of the optical fiber, chemical resistance, and sufficient adhesion to the primary coating.
To achieve the desired characteristics, conventional secondary coating compositions generally contain urethane-based oligomers in large concentration with monomers being introduced into the secondary coating composition as reactive diluents to lower the viscosity. Because conventional oligomeric components are, in general, much more expensive than the monomeric components, the use of oligomers in high concentration has the effect of increasing the cost of producing secondary coating compositions as well as the resulting optical fiber. Despite the cost of using oligomeric components in high concentration, it is believed that there are no commercially viable secondary coating compositions that either contain a low concentration or are completely devoid of oligomeric components.
Thus, there remains a need for suitable secondary coating compositions which can be prepared at lower cost than conventional secondary coating compositions and yield secondary coatings with a suitable modulus and other physical properties. The present invention is directed to overcoming this deficiency in the art.
There is also a need for a coating that will reduce the sensitivity of the fiber to bending, particularly micro bending. This is especially relevant for high data rate optical fiber. A high data rate fiber is typically a single mode fiber with a large effective area. Fibers with a large effective area have an increased signal mode transmission capacity in comparison to non-large effective area fibers. However, fibers with a large effective area have a greater sensitivity to stresses, such as stresses caused by bending the fiber. These stresses can lead to distortion of the optically active region of the fiber and result in microbend signal attenuation.
One embodiment of the present invention relates to a composition for coating optical fibers. The composition includes an oligomeric component present in an amount of about 15 weight percent or less and a monomeric component present in an amount of about 75 weight percent or more, where the monomeric component includes two or more monomers when the composition is substantially devoid of the oligomeric component and the cured product of the composition has a Young""s modulus of at least about 650 MPa.
Another embodiment of the present invention relates to a coating or matrix material which is the cured product of a composition of the present invention that includes an oligomeric component present in an amount of about 15 weight percent or less and a monomeric component present in an amount of about 75 weight percent or more. The-coating or matrix material is characterized by a Young""s modulus of at least about 650 MPa.
Another embodiment of the present invention relates to an optical fiber that includes a glass fiber, a primary coating encapsulating the glass fiber, and a secondary coating encapsulating the primary coating. The secondary coating is the cured product of a composition that includes an oligomeric component present in an amount of about 15 weight percent or less and a monomeric component present in an amount of about 75 weight percent or more. The secondary coating is characterized by a Young""s modulus of at least about 650 MPa.
A further embodiment of the present invention relates to a method of making an optical fiber of the present invention. The method includes the steps of providing a glass fiber having a primary coating, applying to the coated glass fiber a composition that includes an oligomeric component present in an amount of about 15 weight percent or less and a monomeric component present in an amount of about 75 weight percent or more, and exposing the coated glass fiber to conditions sufficient to cause polymerization of the composition to form a secondary coating. The secondary coating is characterized by a Young""s modulus of at least about 650 MPa.
An alternative method of making an optical fiber of the present invention includes the steps of providing a glass fiber coated with a first composition, applying to the coated glass fiber a second composition that includes an oligomeric component present in an amount of about 15 weight percent or less and a monomeric component present in an amount of about 75 weight percent or more, and exposing the coated glass fiber to conditions sufficient to cause polymerization of the first and second compositions to form a primary coating and a secondary coating. The secondary coating is characterized by a Young""s modulus of at least about 650 MPa.
Yet another embodiment of the present invention relates to a fiber optic ribbon that includes a plurality of substantially planar, substantially aligned optical fibers and a matrix encapsulating the plurality of optical fibers, where the matrix has a Young""s modulus of a least about 650 MPa and is the cured product of a composition that includes an oligomeric component present in an amount of about 15 weight percent or less and a monomeric component present in an amount of about 75 weight percent or more.
An additional embodiment of the invention relates to a composition which includes an oligomeric component present in an amount of more than about 15 weight percent and a monomeric component present in an amount of less than about 82 weight percent. The cured product of the composition has a Young""s modulus of at least about 900 MPa.
Another additional embodiment of the invention relates to an optical fiber that includes a glass fiber, a primary coating encapsulating the glass fiber, and a secondary coating encapsulating the primary coating. The secondary coating is a cured product of the composition that includes the oligomeric component in more than 15 weight percent and the monomeric component in an amount less than 82 weight percent. The secondary coating is characterized by a Young""s modulus of at least about 900 MPa.
Embodiments of the invention also include a method of making an optical fiber. The aforementioned secondary coating including more than about 15 weight percent of the oligomeric component is applied to an optical fiber. The optical fiber is already coated with a primary coating. The secondary coating is exposed to conditions to cause the secondary coating to polymerize. In an alternative inventive method, both the primary coating and the secondary coating are exposed to conditions sufficient to cause each respective coating to polymerize.
Embodiments of the invention also include the application of the aforementioned secondary coatings having a Young""s modulus of at least about 900 MPa to a large effective area fiber.
The composition of the present invention has suitable characteristics which enable its use in preparing the outer coating material on optical fibers and the matrix material on fiber optic ribbons. Moreover, when cured, the composition results in a coating or matrix material that possesses desirable characteristics with respect to water absorption, reduced microbend sensitivity, and extraction, as well as strength or modulus. Thus, suitable coating or matrix materials can be prepared from a composition that contains little or no oligomeric components, which significantly reduces the cost of preparing such compositions as well as the optical fibers and fiber optic ribbons that contain the cured product of such compositions.